Light-emitting device and optical transmission unit

ABSTRACT

A light-emitting device includes 16 vertical-cavity surface-emitting laser diodes (VCSELs) disposed like a 4×4 grid, for example, in a sufficiently narrower range than the end surface of an optical fiber. The 16 VCSELs disposed in the light-emitting device emit optical signals in the same direction. Since the VCSELs are disposed with a concentration in the sufficiently narrower range than the end surface of the optical fiber as described above, if the optical signals emitted from the VCSELs are spread, almost all optical signals generated by the light-emitting device are incident on the end surface of the optical fiber and are transmitted through the optical fiber.

[0001] The present disclosure relates to the subject matter contained inJapanese Patent Application No.2001-348702 filed on Nov. 14, 2001, whichis incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION DETAILED DESCRIPTION OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a light-emitting device and an opticaltransmission unit for converting an electric signal into an opticalsignal and transmitting the optical signal.

[0004] 2. Description of the Related Art

[0005] As a device for converting an electric signal into an opticalsignal, for example, a vertical-cavity surface-emitting laser diode(VCSEL) is in the actual use.

[0006] The VCSEL has the characteristics of small threshold current ascompared with an end surface light-emitting laser diode and being easilyput into an array.

[0007] Generally, the VCSEL has the features of low output as comparedwith a general laser diode and life shortened in proportion to thesquare or the cube of a current value if a drive current is increased.

[0008] For example, JP-A-7-38205 (Document 1) discloses a technique ofgenerating an optical signal using a plurality of face light-emittinglaser diodes.

[0009] However, in the technique disclosed in Document 1, a plurality offace light-emitting laser diodes each having a horizontal resonator, awaveguide, and a diffraction grating need to be disposed so that opticalsignals emitted from the face light-emitting laser diodes are gatheredat one point, and it is hard to manufacture.

[0010] For example, JP-A-9-18423 (Document 2) discloses a laser diodearray using a plurality of VCSELs for emitting different lightwavelengths, a collimator array, and a condensing lens.

[0011] The laser diode array disclosed in Document 2 is used to transmitan optical signal by wavelength division multiplexing, and does notsolve the problems of low output of VCSEL and shortening the life if thedrive current is increased.

SUMMARY OF THE INVENTION

[0012] It is therefore an object of the invention to provide alight-emitting device capable of making up for the lowness of output ofeach vertical-cavity surface-emitting laser diode (VCSEL) and shorteningof the life of the VCSEL if a drive current is increased and an opticaltransmission unit using the light-emitting device.

[0013] It is also an object of the invention to provide a light-emittingdevice of an array structure of a simple structure and an opticaltransmission unit using the light-emitting device.

[0014] [Light-emitting Device]

[0015] To the ends, according to the invention, there is provided alight-emitting device including a plurality of vertical-cavitysurface-emitting laser diodes for emitting an optical signal in the samedirection and a drive circuit for driving the plurality ofvertical-cavity surface-emitting laser diodes by the same signal.

[0016] [Optical Transmission Unit]

[0017] According to the invention, there is provided an opticaltransmission unit including a light-emitting device and a light guidefor receiving an optical signal emitted from the light-emitting deviceat one end and transmitting the optical signal to another end. Thelight-emitting device includes a plurality of vertical-cavitysurface-emitting laser diodes for emitting optical signals in the samedirection and a drive circuit for driving the plurality ofvertical-cavity surface-emitting laser diodes by the same signal. Theoptical signals of the plurality of vertical-cavity surface-emittinglaser diodes are transmitted through the light guide.

[0018] Preferably, the light-emitting device emits an optical signal tothe one end of the light guide, which faces to an emission surface ofthe plurality of vertical-cavity surface-emitting laser diodes. Also,the plurality of vertical-cavity surface-emitting laser diodes aredisposed in an area of the one end of the light guide.

[0019] Preferably, the plurality of vertical-cavity surface-emittinglaser diodes are disposed like a grid.

[0020] Preferably, one of the plurality of vertical-cavitysurface-emitting laser diodes is disposed like a coaxial.

[0021] Preferably, the light guide includes an optical dividing typelight guide using a sheet-like light guide-for splitting the opticalsignal and a plurality of optical transmission lines for transmittingthe split optical signals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the accompanying drawings:

[0023]FIGS. 1A and 1B are drawings to show the positional relationshipbetween a first light-emitting device and VCSELs according to theinvention and the light incidence surface of an optical fiber;

[0024]FIG. 2 is a circuit diagram of the light-emitting device shown inFIG. 1;

[0025]FIG. 3 is a drawing to show an outline of the structure of eachVCSEL shown in FIGS. 1 and 2;

[0026]FIG. 4 is a drawing to show the configuration of a secondlight-emitting device and an optical transmission unit using thelight-emitting device according to the invention; and

[0027]FIG. 5 is a drawing to show the configuration of a thirdlight-emitting device according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Referring now to the accompanying drawings, there is shown apreferred embodiment of the invention.

[0029]FIGS. 1A and 1B are drawings to show the positional relationshipbetween a first light-emitting device 1 and VCSELs 2 thereof accordingto the invention and a light incidence surface of an optical fiber 3.FIG. 1A is a front view. FIG. 1B is a sectional view taken on line A-A′in FIG. 1A.

[0030] In FIG. 1A, for simplicity, only one of n (n≧2; in FIGS. 1 and 2,n=16) VCSELs 2 is denoted by the reference numeral 2.

[0031] As shown in FIG. 1A, in the light-emitting device 1, the 16vertical-cavity surface-emitting laser diodes (VCSELs) 2 are disposedlike a 4×4 grid, for example, in a sufficiently narrower range than theend surface of the optical fiber 3.

[0032] As shown in FIG. 1B, the 16 VCSELs 2 disposed in thelight-emitting device 1 emit optical signals in the same direction.

[0033] Since the VCSELs 2 are disposed with a concentration in thesufficiently narrower range than the end surface of the optical fiber 3as described above, if the optical signals emitted from the VCSELs 2 arespread as indicted by dotted lines in FIG. 1B, almost all opticalsignals generated by the light-emitting device 1 are incident on the endsurface of the optical fiber 3 and are transmitted through the opticalfiber 3.

[0034]FIG. 2 is a circuit diagram of the light-emitting device 1 shownin FIG. 1.

[0035] As shown in FIG. 2, differential signals from the outside aregiven to the light-emitting device 1.

[0036] A laser diode driver (LDD) 10 generates the same drive signal forVCSELs 2-1 to 2-n (2-16) from one differential input signal, andsupplies {fraction (1/16)} equally to each of the VCSELs 2-1 to 2-16.

[0037]FIG. 3 is a drawing to show an outline of the structure of eachVCSEL 2 shown in FIGS. 1 and 2.

[0038] As shown in FIG. 3, the VCSEL 2 is made up of layers such as anupper electrode 200, an interlayer insulating film 202, a verticalresonance section 22, a GaAs substrate 230, and a lower electrode 232.The vertical resonance section 22 is made up of layers such as a contactlayer 220, an upper DBR layer 222, and an AlAs layer 224.

[0039] As shown in FIGS. 2 and 3, each of the VCSELs 2-1 to 2-16converts the same drive signal supplied from the LDD 10 into an opticalsignal and emits the optical signal from an emission port 204. As shownin FIG. 1B, as the whole of the VCSELs 2-1 to 2-16, one optical signalis made incident on the end surface of the optical fiber 3.

[0040] As the optical fiber 3, an optical fiber having a comparativelylarge diameter, for example, a plastic optical fiber of φ0.5 to 1 mm ispreferred, in which case the grid pitch of the VCSELs 2-1 to 2-16 may beten several pm to several tens μm.

[0041] If the light-emitting diode 1 is thus configured, the drivecurrent flown into each of the VCSELs 2-1 to 2-16 can be made about{fraction (1/16)} as compared with the case where one VCSEL 2 is used.

[0042] The life of the VCSEL is shortened in proportion to the square orthe cube of the drive current value. Thus, if about {fraction (1/16)} ofthe current value is used for each of the 16 VCSELs 2-1 to 2-16, thelife of each of the VCSELs 2-1 to 2-16 can be extended to severalhundred times as compared with the case where one VCSEL 2 is used.

[0043] The temperature rise of the VCSEL 2 can be lessened and the lifeof the VCSEL 2 can be furthermore prolonged.

[0044] Since large number of VCSELs 2 are used to generate one opticalsignal, it can compensate for the lowness of output when a single VCSEL2 is used.

[0045] Since the light-emitting diode 1 may include the VCSELs arrangedsimply like a grid, the structure is very simple and easy.

[0046] [First Modification]

[0047]FIG. 4 is a drawing to show the configuration of a secondlight-emitting device 4 and an optical transmission unit 5 using thelight-emitting device 4 according to the invention.

[0048] Also in FIG. 4, for simplicity, only one of 16 VCSELs 2 isdenoted by the reference numeral 2 as with the light-emitting device 1(A).

[0049] As shown in FIG. 4, the optical transmission unit 5 is made up ofthe light-emitting device 4, a sheet-like light guide (optical dividingtype light guide) 6, and k (k≧2; in FIG. 4, k=4) optical fibers 3-1 to3-k (3-4).

[0050] The sheet-like light guide 6 is manufactured by forming anacrylic resin like a sheet, for example, for accepting an optical signalgenerated by the light-emitting device 4 from a surface where thelight-emitting device 4 is disposed.

[0051] The sheet-like light guide 6 scatters the optical signal acceptedfrom a surface (incidence surface) facing to an emission port 204 of theVCSEL 2 of the light-emitting device 4 (FIG. 3) and guides the opticalsignal to an opposed surface of the sheetlike guide 6 to guide to andmake the optical signal incident on a light incidence surface of theoptical fibers 3-1 to 3-4.

[0052] The optical fibers 3-1 to 3-4 transmit the optical signal emittedfrom the surface (emission surface) facing to the incidence surface ofthe sheet-like light guide 6.

[0053] The circuit configuration of the light-emitting device 4 is thesame as that of the light-emitting device 1 shown in FIG. 2. In thelight-emitting device 4, a set of the 16 VCSELs 2 is disposed like a 2×8grid in a narrower range than the incidence surface of the sheet-likelight guide 6 so that the set of the VCSELs 2 becomes a shape suitablefor the incidence surface of the sheet-like light guide 6.

[0054] The light-emitting device 4 is disposed in the proximity of thesheet-like light guide 6 or is placed in intimate contact with thesheet-like light guide 6 so that the emission ports 204 of the 16 VCSELs2 (FIG. 3) face to the incidence surface of the sheet-like light guide6.

[0055] According to the optical transmission unit 5, the optical signalgenerated by the light-emitting device 4 can be accepted efficiently bythe sheet-like light guide 6 for dividing the optical signal and guidingthe optical signal into the optical fibers 3-1 to 3-4 for transmission.

[0056] [Second Modification]

[0057]FIG. 5 is a drawing to show the configuration of a thirdlight-emitting device 7 according to the invention.

[0058] Also in FIG. 5, for simplicity, only one of a plurality of VCSELs2 is denoted by the reference numeral 2.

[0059] As shown in FIG. 5, the light-emitting device 7 includes oneVCSEL 2 placed at a position facing to the center of an optical fiber 3.

[0060] Further, the light-emitting device 7 includes m (m24 1; in FIG.5, m=6) VCSELs 2 placed on the circumference of a circle sufficientlynarrower than the end surface of the optical fiber 3 with the one VCSEL2 being the center thereof, as indicated by the dotted line in FIG. 5.

[0061] In addition to disposition of the VCSELs 2 like a grid, if theVCSELs 2 are disposed as shown in FIG. 5, similar advantages to those ofthe light-emitting device 1, 4 can also be provided.

[0062] As described above, the light-emitting device and the opticaltransmission unit using the light-emitting device according to theinvention make it possible to make up for the lowness of output of eachvertical-cavity surface-emitting laser diode (VCSEL) and shortening ofthe life of the VCSEL if the drive current is increased.

[0063] The structures of the light-emitting device and the opticaltransmission unit using the light-emitting device according to theinvention are simple.

What is claimed is:
 1. A light-emitting device comprising: a pluralityof vertical-cavity surface-emitting laser diodes for emitting an opticalsignal in the same direction; and a drive circuit for driving theplurality of vertical-cavity surface-emitting laser diodes by the samesignal.
 2. An optical transmission unit comprising: a light-emittingdevice; and a light guide for receiving an optical signal emitted fromthe light-emitting device at one end and transmitting the optical signalto another end, wherein the light-emitting device includes: a pluralityof vertical-cavity surface-emitting laser diodes for emitting opticalsignals in the same direction; and a drive circuit for driving theplurality of vertical-cavity surface-emitting laser diodes by the samesignal; and wherein the optical signals of the plurality ofvertical-cavity surface-emitting laser diodes are transmitted throughthe light guide.
 3. The optical transmission unit according to claim 2,wherein the light-emitting device emits an optical signal to the one endof the light guide, which faces to an emission surface of the pluralityof vertical-cavity surface-emitting laser diodes; and wherein theplurality of vertical-cavity surface-emitting laser diodes are disposedin an area of the one end of the light guide.
 4. The opticaltransmission unit according to claim 3, wherein the plurality ofvertical-cavity surface-emitting laser diodes are disposed like a grid.5. The optical transmission unit according to claim 3, wherein one ofthe plurality of vertical-cavity surface-emitting laser diodes isdisposed like a coaxial.
 6. The optical transmission unit according toclaim 2, wherein the light guide includes: an optical dividing typelight guide using a sheet-like light guide for splitting the opticalsignal; and a plurality of optical transmission lines for transmittingthe split optical signals.